1. Field of the Invention
This invention relates generally to the fields of hypervelocity impact shielding and to the deployment of such shields. Specifically, the present invention relates to apparatuses and methods to deploy protective hypervelocity shields adjacent exposed portions of a space vehicle for preventing damage to the vehicle caused by impact with meteoroids and orbiting particles.
2. Description of the Related Art
Because of the possibility of damage to space vehicles and orbiting satellites caused by meteoroids and orbital debris that may impinge upon the vehicles at very high relative velocities, shielding structures for protecting such space vehicles are an important design consideration. In the case of orbital vehicles, such as satellites, there is a danger of collision with debris that remains in earth orbit after being released from various spacecraft. Such debris may have originated from the fragmentation or break up of portions of orbiting spacecraft, e.g., from particles released in connection with the inadvertent detonation of spacecraft propulsion system components or the like.
Debris may remain in orbit for extended periods and the probability of damage to spacecraft and orbiting satellites is thus greater than was the case in the early phases of space exploration prior to the accumulation of such space debris over the years. Orbiting spacecraft or satellites may approach and impact such orbital debris traveling at relative velocities of 10 kilometers per second or greater and the debris particles therefore impact such orbiting spacecraft with substantial energy. The kinetic energy of such a particle as it impacts upon an orbiting vehicle is, of course, proportional to its mass and to the square of its velocity relative to the vehicle.
Additionally, the threat from incoming meteoroids is also of concern. Meteoroids may approach the space vehicle at even greater relative velocities than man-made, orbital debris particles, but they are less frequently encountered than are the increasingly common man-made debris for spacecraft in low Earth orbit; i.e., at altitudes less than 1500 kilometers above the Earth""s surface. In the description to follow, the term xe2x80x9cparticlexe2x80x9d should be understood to refer both to man-made particles and meteoroids, and the term xe2x80x9chypervelocityxe2x80x9d refers to relative velocities of two kilometers per second or greater. The term xe2x80x9cparticlexe2x80x9d is used to refer to objects of diameters up to 10 centimeters in diameter. Typically, the orbits for debris objects greater than 10 centimeter in diameter are tracked by ground radar systems, permitting active spacecraft the necessary information to perform maneuvers away from potential collisions with tracked objects.
Additionally, man-made space debris can remain in orbit for extended periods and such debris is largely concentrated in altitude regions commonly used by orbiting vehicles and satellites. The impact of space debris against orbiting satellites, or, alternately, the impact of the orbiting satellite against a debris particle, also may tend to break up the debris particle thereby generating a quantity of smaller secondary debris fragments all of which also remain in orbit. This constitutes additional potential hazards to orbiting spacecraft and satellites.
Orbital debris particles and meteoroids are of widely differing sizes, and their diameters may typically range from 0.01 cm to 1.0 cm or greater. Those of less than several centimeters in diameter are generally too small for electro-optical tracking and avoidance maneuverance. However, if they are of sufficient size and density, such orbital debris particles and meteoroids may have sufficient energy to compromise critical components or systems of a spacecraft, or penetrate the space suits of astronauts engaged in extravehicular activities.
As will be appreciated by those in the art, any apparatus or system for protecting an orbital vehicle from space debris and meteoroids must be evaluated both in terms of its effectiveness in breaking up particles of given ranges of densities and velocities and of its size and weight. Obviously, the additional weight entailed in such shielding structures reduces the effective payload of the spacecraft. Because of the very high costs per kilogram of launching a structure into earth orbit or beyond, weight limitations are a major consideration in spacecraft design. Thus, protection against orbital debris could be provided by the use of a single wall, i.e., monolithicxe2x80x3 shield, of heavy sheet material of sufficient density and thickness. For example, protection against substantially all orbiting debris of diameter less than 0.3 centimeters could be achieved through the use of a single steel wall that is 1.3 cm thick.
However, the weight of such a vehicle would render it impractical for space application and would reduce the available payload substantially. Thus, the walls and bulkheads of most space vehicles are typically of aluminum or various lightweight alloys and are normally about 0.25 inches (0.6cm) or less in thickness. Such wall structures are structurally adequate for most applications where they typically provide the ability to contain gases and liquids under pressure. For instance, the inner wall or pressure shell of the inhabited modules on space stations such as Mir or those on the International Space Station vary from 0.2 cm to 0.6 cm thick. Similar construction exists for propellant tanks and pressurized gas carriers.
Although these pressure vessels are more than adequate from a structural standpoint, they are susceptible to penetration by meteoroids and debris particles of diameters greater than 0.1 centimeters, particularly in the case of particles or projectiles of materials denser than that of the wall structure itself. Accordingly, the field has sought to provide shield structures adapted for protection from larger meteoroid and orbital debris particles, i.e., particles up to 2 centimeters diameter, to be deployed adjacent and in covering relationship with space craft and satellite wall structures exposed to such debris for minimizing the danger of penetration by impinging particles.
A crucial consideration with respect to the design of such shielding structures is the density of the impacting particles. Although aluminum shielding and aluminum wall structures are generally effective against relatively light-weight particles, such as space debris of aluminum, or relatively light, non-metallic meteoroids, they provide substantially less protection against denser debris particles such as fragments of steel, copper, nickel alloys, and the like. Such hazards- from high-density debris have not generally been taken into account in the design of spacecraft and satellites currently in use. In the future, however, the potential for damage to space craft caused by impact with high-density hypervelocity particles is expected to be of increasing concern, particularly for missions of extended duration and at particular altitudes.
In the past, shielding structures of enhanced effectiveness were provided by the use of one or more xe2x80x9cbumperxe2x80x9d sheets. Such multi-layer shield designs serve to increase the effectiveness of the shielding over that of a single, monolithic wall of equivalent weight. An outer bumper sheet is typically deployed in spaced relation to a heavier, back sheet that may constitute the inner wall or critical component of the spacecraft that requires protection from impact damage. The bumper sheet is spaced from the back plate by a standoff distance on the order of several centimeters. The function of the bumper sheet is to break up any impinging particle into a cloud of fragmented and partially molten and/or vaporized material of lower energy level per unit of surface area and reduced penetrating power than that of the incoming particle itself.
Such shield or multi-layer shield structures include those known as xe2x80x9cWhipple shields,xe2x80x9d after the originator. Aluminum alloys have been typically used for both the bumper sheets and the back plates of such structures. Additionally, multiple layers of insulative material, in the form of 10 to 30 separate aluminized mylar or kapton foil sheets, may be included in the structure, typically sandwiched between the bumper shield and the back plate, for thermal control and insulation. Optimal shielding dimensions for such structures are dependent upon the geometry and mass of the object to be protected, but generally, the ratio of the standoff spacing of the outer bumper and the diameter of incoming particles will be in the order of 30:1 or greater.
U.S. Pat. No. 5,601,258 discloses a spacecraft shield having one or more bumper elements, a cloud stopper element located within the bumper element and a fragment stopper element which is located within the cloud stopper element. This shield of U.S. Pat. No. 5,601,258 completely encloses the spacecraft and is permanently mounted either on main structures of the spacecraft or at hardpoint end structures of the spacecraft. The impacting particles are successively fragmented, possibly vaporized, and dispersed over a wider area or stopped at a layer as each layer is encountered in the shield.
A more recent shielding structure is provided in U.S. Pat. No. 6,298,765. The hypervelocity impact shield assembly includes at least one sacrificial impactor disrupting/shocking layer and at least one space-rated open cell foam material positioned between the sacrificial layers with spacing elements therebetween to form a multishock assembly. The assembly is enclosed by a cover and mounted to the spacecraft by such things as snap attachment elements, strap attachment elements or Velcro(copyright) hook and pile fastening attachment elements. The assembly may be flattened after attachment and deployed after launch of the spacecraft to accommodate more payload.
Accordingly, the inventors have recognized a need in the art for an effective apparatus and method of deploying shielding structures on spacecraft. More specifically, the prior art is deficient in an apparatus and method of deploying a hypervelocity shield on-orbit, yet which do not entail substantial weight penalties which would substantially reduce available payload. The present invention fulfills this longstanding need and desire in the art.
In one embodiment of the present invention, there is provided an apparatus for deploying a hypervelocity shield on a structure in exoatmospheric space. The hypervelocity shield may comprise a mesh formed of wires of a ductile material where at least one of the wires optionally is a shape-memory alloy and a supporting matrix formed of strands of a material that has a density less than that of the ductile material. The strands of the supporting matrix may be interwoven with the mesh and thus comprise a means for supporting the mesh in a predetermined configuration.
The apparatus also comprises a frame structure attached to at least one edge of the hypervelocity shield and further has an insulated electric cable to deploy the hypervelocity shield. The frame structure provides support for the hypervelocity shield. Optionally, the frame structure may be insulated and formed of the shape-memory alloy. The instant apparatus also has a means of operably attaching the hypervelocity shield to the structure.
In another embodiment of the present invention, there is provided an apparatus to deploy at least one hypervelocity shield on a structure in exoatmospheric space. The hypervelocity shields described herein are wound on rolls. The apparatus further comprises a shield storage cassette which can store at least one of the rolled shields and has a cover on its front face. The shields are attached to a back face of the cassette cover. The apparatus further has a mast storage canister rotatably mounted on the top side of the cassette which contains an extendible/retractable mast; the canister has a cover on the front open face and the mast is attached to the back side of the cover. Additionally, the mast cover is connected to the shield storage cassette cover by a hinging mechanism. Both the mast storage canister and a forward arm of the hinging mechanism rotate in a plane parallel to the plane of the subsequently deployed hypervelocity shields. Furthermore, the apparatus can be attached to the structure via two mounting attach points on both the mast storage canister and the shield storage cassette cover.
In yet another embodiment of the present invention there are provided methods of deploying hypervelocity shields described herein using the apparatuses described herein.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.